Kling was a population center or location within the Klingon Empire. This place was located in the Alpha Quadrant. Its location in the Milky Way Galaxy was depicted on a Federation star chart in 2293. (Star Trek VI: The Undiscovered Country, production art)
According to the Star Trek Encyclopedia: "At the time the episode was written, Kling was intended as the name of the Klingon Homeworld. Once the episode was filmed, it was realized that the name sounded pretty silly, so later scripts simply referred to "the Homeworld." The only time the Homeworld was given a name was in Star Trek VI: The Undiscovered Country, when it was called Qo'noS, pronounced "kronos."" Of course, since this passage originally appeared in the Encyclopedia, the term "Qo'noS" has been referenced on numerous occasions.
Consequently, Kling has been referenced in the Star Trek Encyclopedia as a "A district or city on the Klingon Homeworld."
"The Explored Galaxy"
"The Explored Galaxy" was a map of charted space in the Alpha Quadrant. Kling was located between the Tholian Assembly and Romulus. Both locations were identified in DS9: "The Search, Part II", "Call to Arms" as being located in this quadrant. The chart was also seen in several Star Trek: The Next Generation and Star Trek: Deep Space Nine episodes set in the 24th century, from the year 2364 to 2370. These were TNG: "Conspiracy", "The Measure Of A Man", "The Emissary", "The Mind's Eye", "The Game", and DS9: "In the Hands of the Prophets", "Cardassians".
Kling was an alternate name for Qo'noS. (pg. 55)